%%
%% The LaTeX Companion, 3ed
%%
%% Example 8-4-4 on page I-617 in "Inner box geometry".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{183.0pt}

%StartShownPreambleCommands
\usepackage{lipsum,tcolorbox}
\tcbset{top=0pt,bottom=0pt,left=5pt,lefttitle=20pt,
        rightlower=0pt,rightrule=15pt}
%StopShownPreambleCommands

\begin{document}
\begin{tcolorbox}[title=A box title,middle=0pt]
  \lipsum[1][1] \tcblower \lipsum[1][2]
\end{tcolorbox}
\end{document}
